1. Field of the Invention
The invention relates to a multi-ply tissue paper product comprising at least three structured plies of paper and a method for producing same.
2. Description of Related Art
Multi-ply tissue paper for various uses as a kitchen paper, toilette paper or handkerchief involves a plurality of plies of paper which are bonded together to form a multi-ply paper.
General goals with respect to multi-ply paper are to provide softness, an improved feel, good mechanical strength and the desired absorption properties.
In multilayer products, tissue plies can be structured by different methods. A first method for providing a structured ply of paper is the use of a TAD (through air drying) process, which gives the paper a three-dimensional structure already in the paper machine.
A further method involves the embossing of tissue using a single nip or multi-nip embossing. The ply bonding of the single plies is provided by a mechanical embossing or by using an adhesive. In the case of three or multi-ply products, a plurality of plies are generally embossed together to provide a volume to the product. However, the embossing usually hardens the product and contributes to a rough feeling of the product. On the other hand, it is possible to use a micro embossing with a high density of protuberances of more than 40 protuberances/cm2. A micro embossed product feels soft. However, micro embossed paper feels as if it could not absorb enough liquid.
Therefore, there is a constant desire to provide a tissue product with a high softness surface and a sufficient bulk.
WO 99/45205 describes a multi-ply tissue product with two embossed outer plies and a middle ply without embossing. The outer plies are embossed so that the protuberances are arranged with a density of more than 30 protuberances/cm2. Each of the outer plies is glue bonded to the middle ply.
U.S. Pat. No. 5,382,464 and U.S. Pat. No. 5,736,223 both relate to specific nested configurations of a three-ply, embossed paper. The multi-ply paper according to U.S. Pat. No. 5,736,223 is composed of two external plies, the embossing protuberances of which are arranged in a foot-to-foot configuration. A third embossed middle ply is provided, the embossing protuberances of which nest between the protuberances of one of the two external plies. U.S. Pat. No. 5,382,464 uses a different approach by providing embossed plies having protuberances of two different heights wherein the protuberances having a greater height alternate with more shallow protuberances. When the embossed ply is used to form a multi-ply paper, the small protuberances are arranged in a foot-to-foot configuration with the protuberances of a second embossed ply, so that the big protuberances of the first ply are positioned to nest between the protuberances of the second ply.
It is an object of the invention to provide a multi-ply tissue paper which combines in an advantageous way a high softness and a necessary bulk to provide a good feeling to the user. Moreover, the product should be appealing to the eye.
In one embodiment of the invention, there are at least three embossed plies of paper. Both outer plies are provided with a microstructure pattern with protuberances with a density (concentration) of more than 40 protuberances per cm2. At least one middle ply sandwiched between the outer plies is provided with a third structure pattern being an embossing pattern with a density of the protuberances of less than 40 protuberances per cm2. By bonding the outer, microstructured plies and the embossed middle ply together, the resulting multi-ply tissue paper combines soft outer plies and a volume producing middle ply. The resulting tissue paper combines the advantages of high softness, a high volume and a good ply bonding. Due to the volume generating embossing of the middle ply, there is a considerable saving of fibres which contributes to the cutting down of the production costs.
Another embodiment of the invention includes a method of producing a multi-ply tissue paper comprising the steps of structuring a first outer ply with a first microstructure pattern which has a first density of protuberances, the structuring of a second outer ply with a second microstructure pattern with a second density of the embossed protuberances and the embossing of a middle ply with a third structure pattern being an embossing pattern. Whereas the first and second pattern has a density of more than 40 protuberances per cm2, the third pattern has a density of less than 40 protuberances per cm2. When combining together the three plies so that the third pattern is in an unregistered way, the middle ply imparts volume to the multi-ply tissue whereas the two outer plies with the microstructure pattern contribute to the softness of the product.
According to a preferred embodiment, the first protuberances of the first microstructure pattern have a first height h1 and the second protuberances of the second microstructure pattern have a second height h2, wherein the protuberances of the third structure pattern have a height H which is at least 1.3 times greater than h1 and h2, respectively, preferably at least 1.5 times greater and most preferably at least 2.0 times greater than h1 and h2. This is a further measure to impart bulk to the middle ply and to a multi-ply tissue paper product.
Preferably, the first outer ply has a fourth structure pattern, preferably an embossing pattern with fourth protuberances having essentially the same height as the first protuberances of the first microstructure pattern. These fourth protuberances can be arranged so that a decorative pattern is formed which is appealing to the eye of the user. The same is possible for the second outer ply which can have a fifth structure pattern, preferably an embossing pattern with protuberances having essentially the same height as the second protuberances of the second microstructure pattern. It is possible to provide a free combination of multi-ply tissue paper with a decorative pattern on one or both outer surfaces. The fourth and fifth structure pattern can be essentially identical or can be different.
According to the preferred embodiment of the invention, the ply bonding is generated by glue lamination using a lamination pattern. The height of the lamination pattern must be the sum of the individual heights of the microstructure pattern of the outer plies (h1+h2) and the height of the third pattern (H). This ply bonding technique using a separate lamination pattern can be used to provide a design lamination to the product. It is possible to use, e.g., discreet design lamination dots which are arranged to resemble the shape of a desired design like a flower. In order to provide a good ply bonding in the inventive multi-ply tissue paper, the glue lamination is preferably deep embossed to provide a sufficient ply bonding despite of the volume embossed middle ply.
The adhesives used can be any adhesives usually used in the art, e.g., starch or polyvinylalcohol.
According to an alternative embodiment of the invention, the ply bonding is generated by a mechanical ply bonding technique. Such a mechanical ply bonding technique could be the pressing of the multi-ply tissue with some small protrusions on a roller, like needle-tips. These protrusions run with high pressure against a suitable anvil roller. This pressing provides for a ply bonding between the individual tissue paper plies. An example for such a mechanical ply bonding is edge embossing.
According to the preferred embodiment of the invention, the fourth and/or fifth protuberances have an elongate shape. With such an elongate shape, it is possible to provide a design pattern which is easier to discern for a user and, thus, more complicated designs can be provided on the same scale of the design pattern compared to the use of single dots to generate a design pattern.
However, the alternative use of fourth and/or fifth protuberances with a dot-like-shape is also possible if these protuberances are arranged in a way to form an aesthetic pattern.
According to preferred embodiments of the inventive method, the step of combining together the three plies so that the protuberances lie in an unregistered way can be carried out by first combining the first outer ply and the middle ply to a combined tissue web, the applying of a laminating agent to the combined tissue web and the marrying of the combined tissue web and the second outer ply. As outlined above, the lamination can be provided according to a preferred embodiment of the invention using a design pattern of lamination dots.
In the above described embodiments, at least one of the first and second outer plies is micro-embossed. Alternatively, one of the first and second outer plies is structured by a TAD process. In other words, all combinations of outer plies which are structured by a TAD process or micro-embossed are within the scope of the invention.